Cracking of hydrocarbon oils



Patented Sept. 22, 1942 CRACKIN G OF HYDBOCARBON OILS Joseph V.Marancik, Roselle, and Homer Z. Martin, Elizabeth, N. J., assignors toStandard Oil Development Company, a corporation of Delaware ApplicationAugust 26, 1939, Serial No. 292,002

4 Claims.

This invention relates to the cracking of hydrocarbon oils to form lowerboilingmotor fuel, and pertains more particularly to the cracking ofsuch oils wherein a powdered catalyst is suspended in the oil to becracked and the suspension passed through the cracking zone.

It has heretofore been proposed to crack higher boiling oils into lowerboiling products suitable for motor fuel in the presence of adsorptivecracking catalysts such as activated clays, synthetic gels havingsimilar chemical components and the like.

According to one mode of operation, the oil to be cracked, preferably invapor form, s passed through a cracking zone containing a bed, or aplurality of beds, of catalytic material. During the cracking operationthe catalyst mass rapidly becomes fouled with carbonaceous depositswhich reduces the activity of the catalyst and necessitates frequentregenerations to restore the catalyst activity. In such operations, itis necessary to interrupt the cracking operation in order to attain theregeneration. This involves stopping the cracking operation, purging thereaction chamber of volatile hydrocarbons, regenerating the resultingcatalyst mass, purging the reaction chamber of regenerating gases andthe return to the cracking cycle.

It; has been observed that when operating such a process, an excessiveamount of low-grade products such as coke and gas is formed at the verybeginning of the cracking cycle such as at the first minute or two ofoperation. In other words, during the early part of the cracking cycle alarge portion of the oil treated is degraded to coke and gas withlittle, if any, formation of gasoline. While the explanation for this isnot fully established, there is reason to believe that it is due to thefact that the initial oil vapors contact an excessive amount of catalystand consequently become over-cracked to gas and coke. As the crackingoperation continues the deposition of coke tempers the activity of thecatalyst so that the tendency of the oil to overcrack diminishes as thecracking operation continues. For example, assume that the operation iscarried out with a feed rate in proportion to the amount of catalystcontained in the reaction chamber of 1.2 volumes of liquid oil pervolume of catalyst per hour. During the first minute and for each minutethereafter .02 volume of oil is treated by the total volume of catalyst.This small volume of oil treated in proportion to the amount of catalystcontained in the reaction chamber may explain why excessive overcrackingoccurs during the initial part of the cycle when the catalyst is mostactive.

It has also been proposed to suspend the catalyst in the oil vapors tobe cracked and to pass the suspension through a cracking zone. Whenoperating in this manner the resident time 0f both the catalyst and theoil vapors within the cracking zone is substantially the same and anygiven quantity of oil vapors can be treated with a denite, xed quantityof catalyst. In this case the tendency of the oil to overcrack can becontrolled by regulating the amount of catalyst added to the oil streamand the resident time of the suspension within the cracking zone.

While this method of operating makes it possible to more eiectvelycontrol the tendency of the oil to overcrack with resulting excessivedegradation of feed stock which is inherent in processes wherein the oilvapors pass through a stationary mass of catalyst, such mode ofoperation, when carried out according to previous practices, is subjectto other disadvantages.

For example, when operating in such manner it has been the practice topass the suspension of powdered catalyst and cracked products issuingfrom the cracking zone through separators to remove the catalystparticles. According to previous practices. the powdered catalyst soremoved was regenerated, and returned to the cracking zone. If thecatalyst is regenerated 'each time it passes through the cracking zone alarge amount of regenerating equipment is necessary for a cracking unitof commercial capacity due to the large number of regenerations to whichthe catalyst is subjected in a given time. Furthermore, there is atendency for the catalyst to lose its activity at a faster rate as thenumber of regenerations to which it is subjected in a given time isincreased. y

One of the principal objects of the present invention is to provide aprocess of the type last mentioned which will not be subject to thedisadvantages just mentioned.

A further object of the invention is to provide a method of cracking oilwith powdered catalyst wherein the number of regenerations of thecatalyst can be reduced and controlled as desired.

Another main object of the invention is to provide a process forcracking hydrocarbon oil wherein the inherent activity of the catalystcan be utilized to better advantage. Other objects and advantages of theinvention will be apparent from the more detailed descriptionhereinafter in which reference-will be made to the accompanying drawingwhich is a partly schematic and partly diagrammatic illustration of anapparatus capable of carrying the invention into effect.

Referring to the drawing, the reference character III designates a feedline having a pump II through which the oil to be cracked is introducedinto the system. The oil treated may be a clean, condensate stock suchas virgin gas oil, or a residual stock such as topped or reduced crude.'Ihe oil introduced through the feed line I is forced by means of pumpII through a preheating and vaporizing coil I2 located in furnace I3.The oil during its passage through heating coil I2 is preferably heatedto a temperature suilicient to vaporize a large percentage of such oil.'I'he outlet temperature of the heating coil may, for example, be in theneighborhood of from '700 F. to 950 F., depending upon thecharacteristics of the feed stock.

'Ihe oil, after passing through the preheating coil I2 is transferredthrough transfer line I4 to a separator I5 wherein vapors separate fromunvaporized residue. If desired, steam or other stripping gas may beintroduced with the oil or into the separator I5 for assisting in thevaporization of the oil. Unvaporized residue separated in the separatorI5 may be withdrawn therefrom through line I6 and rejected from thesystem. Vapor liberated in the separator I5 is removed therefrom throughline I1 and passed to a cracking chamber I8. In cases where cleancondensate stock is employed, the separator I5 may be omitted or theproduct may be by-passed around the separator through line I9.

In accordance with the present invention there is introduced into the.vapor stream passing to the reaction chamber I8 a powdered crackingcatalyst. According to one of the more specific phases of the inventionthe powdered'catalyst so introduced is an unregenerated catalyst whichhas previously passed one or more times through the same or diierentcracking unit. In the preferred embodiment of the invention, suchunregenerated catalyst is that which has previously been employed fortreating a more refractory oil or an oil which is more diillcult tocrack than the fresh feed charged to the unit through line I0. Suchrefractory oil may, for example, comprise a cycle stock from the same ordinerent cracking unit.

The catalyst may comprise, for example, natural or activated clays.synthetic compounds having similar chemical components and the like.

Referring to the drawing, the powdered catalyst is injected into the oilvapor passing to the reaction chamber I8 by means of a suitable feedingmechanism such as through screw conveyor 2| into which catalyst is fedfrom the hopper 22.

The relative amounts of powdered catalyst and oil vapor passing to thereaction chamber I3 may vary over a substantial range depending upon theactivity of the catalyst, the characteristics of the feed stock, thetime of contact of the suspension within the reaction zone and otherfactors. In general, the ratio of catalyst to oil should be in the orderof from 0.3 to 20 parts of catalyst per part of oil by weight,preferably between 0.5 and 3 parts of catalyst per part of oil.

The oil vapor catalyst suspension is passed through the cracking chamberI3 at a rate sufiicient to maintain the catalyst in suspension. Forillustrative purposes, the cracking chamber ing a conical bottomalthough it may take any other desired form such as, for example, anelongated coil. horizontal chamber or the like. The reaction chamber maybe heated if desired to onset radiation losses or to introduce heat intothe suspension.

'I'he suspension of cracked products and catalyst after passing throughthe reaction chamber I3 is passed through line 23 to a suitable solidgas separator such as a cyclone separator 24 in which the powderedmaterial is separated from the cracked vapor. It is preferred to operatethe separator at a temperature sufficient to avoid any substantialcondensation of the cracked products therein so that the powderedcatalyst so separated can be removed therefrom in a relatively dry form.While a single cyclone separator has been shown in the drawing forpurposes of simpliicty, it will -be understood that additional ones maybe provided for eifecting substantially complete removal of the powderedmaterial from the cracked vapors. 'Ihe cracked I8 is shown in the formof a vertical tower hav- 75 products, after separation of the solidcatalyst therefrom, are passed overhead from the cyclone separator 24through lines 25 and 26 to a fractionating tower 2'I in which the vaporsare subjected to fractionation to condense constituents boiling abovethe desired motor fuel. Vapors remaining uncondensed in thefractionating tower 2l are removed therefrom through line 28 and may bepassed to a condenser 29 in which the desired liquid distillate iscondensed. Products from the condenser 29 may be then passed to areceiver 30 wherein normally gaseous products formed in the crackingoperation may be segregated from liquid distillate. The gases soseparated may be released from the system through line 3I having a valve32 for imposing the desired back pressure on the system. Liquiddistillate collected in the receiver 30 may be withdrawn therefromthrough line 32a as a final product of the process.

Returning to the cyclone separator 24, the solid catalyst separated fromthe cracked product therein is withdrawn from the cyclone separatorthrough conduit 33. If desired, a portion of the catalyst so withdrawnmay be returned directly to the catalyst hopper 22 for return to thecracking zone through conduit 34, or apart v or all of the catalyst fromthe cyclone separator 24 may be passed through the line 33 to a purgingzone 36 in which volatile hydrocarbons are removed from the catalyst inany suitable manner such as by steam stripping or by evacuation of thepurging chamber. For example, steam may be introduced into the purgingchamber 3i through line 3l for steam stripping the catalyst containedtherein. The stripping gases may be released from the purging chamber 36through line 33 and introduced into the cyclone separator 24. Thecatalyst, substantially free oi' volatile hydrocarbons, is then removedfrom stripping chamber 36 through conduit 38 leading vto a suitabletransfer mechanism such as screw conveyor 40 which feeds the catalystinto a' stream of regenerating gas containing oxygen introduced into thesystem through line 4I andblower 42. The suspension of catalyst andregenerating gas is then passed through a regenerating chamber 43maintained at a temperature suilicient to ignite the carbonaceousdeposits on the catalyst formed during the cracking operation.ordinarily desirable to control the temperature during regeneration inorder to avoid reducing the activity of the catalyst. For example, in

Itisl connection with naturally active or activated clays, thetemperature of the regenerating zone should be maintained below 1200 F.and preferably below 1000 F. Generally the temperature within theregenerating zone can be readily controlled due to the relatively lowconcentration of carbonaceous deposits on the catalyst. In some cases,however, it may be desirable to regulate the oxygen concentration of theregenerating .gas or to provide suitable cooling means, such as heatexchangers. within the regenerating chamber to control the temperature.

'I'he catalyst is maintained in suspension in the regenerating gaswithin the regenerating chamber 43 for a period to remove thecarbonaceous deposit formed on the catalyst from the cracking operation.

The suspension of regenerating gas and catalyst passes from theregenerating chamber d3 through line 44 to a suitable solid-gasseparator such as cyclone separator 45 in which-the regeneratedcatalysts are separated from the regenerating gases. The regeneratinggas, after separation of the powdered catalyst therefrom,

vmay be rejectedA from the system through line 46.

The regenerated catalyst may be removed from the separator 45 through a,conduit 41 leading to a purging chamber 48 in which theregeneratedcatalyst is stripped of oxygen. To this end'steam may beintroduced into the purging chamber 48 through line 49 and the purgegases vented to the cyclone separator 45 through line 50.

According to one phase of the invention, the regenerated catalyst isutilized for cracking an oil which is more refractory and more difficultto crack than the oil charged to the heating coil l2. Such oil maycomprise, for example, cycle stock segregated in the fractionating tower21 as hereinafter described. When operating in this manner, theregenerated catalyst is fed by means of a. screw conveyor I to acatalyst hopper 52 serving a separate cracking unit processing cyclestock as later described.

If desired, however, a part or all of the regenerated catalyst may bereturned to the hopper 22 through valved conduit 53. It will beunderstood that it is also within the purview of the present inventionto operate with a single cracking circuit in which a part of thecatalyst is recycled to the same circuit. For example, if the recyclecircuit is out of operation or not employed, all the regeneratedcatalyst can be passed to hopper 22 for return to the fresh oil circuit.

Returning to the fractionating tower 21 in which the cracked productsare fractionated, the condensate formed in the fractionating tower 21 iswithdrawn therefrom through line 54 and may be rejected from the systemthrough line 55. According to one of the specific phases of the presentinvention, however, a part or all of the condensate formed in thefractionating tower 21 is passed through lines 54, 56, and pump 51 tothe inlet side of heating coil 58 located in furnace 59. The oil passingthrough the heating coil 58 is heated to a temperature suilicient tovaporize the oil. Vapors from the heating coil 56 may be then passedthrough transfer line 6|) to a second cracking chamber 6|. In case theoil passing to the heating coil 58 contains unvaporizable constituents,the products from the heating coil 58 may be passed to separator 62wherein unvaporized residue may be dropped out of the oil stream andremoved from the separator through line 63. In` such case, the vaporsliberated in the separator 62 pass overhead through line 64 which mergeswith line 6U leading to the cracking chamber 6l.

If desired, fresh oil from an extraneous source may be fed to theheating coil 58 through line 65 and pump 66.

Before passing to the cracking chamber 6l there is injected into the oilvapors to be cracked fresh or regenerated catalyst from hopper 52. Suchcatalyst may be introduced into the oil vapor through a suitable feedingmechanism such as a screw conveyor 61. The suspension of oil vapors andcatalyst is passed through the cracking zone 6l at a velocity suflicientto maintain the catalyst in suspension within the vapors. The length ofthe cracking chamber and the velocity of the suspension should becontrolled to give the required contact time to obtain the desiredcracking of the oil into gasoline. The time required for the passage ofthe suspension through the cracking chamber 6I may range from one`second up to a minute or two depending upon the desired conversion, thecharacteristics of the feed stock, the temperature and other factors.The cracking zone should be maintained above active cracking temperaturesuch as from '150 F. to 1000 F.

The suspension of the cracked product and catalyst after passing throughthe cracking chamber 6I is transferred through line 68 to a suitablesolid-gas separator such as cyclone separator 69 wherein the powderedcatalyst is removed from the oil vapors. The separator 69 is alsopreferably maintained under a temperature which will avoid anysubstantial condensation of cracked products. The cracked products afterpassing through the cyclone separator 69 are passed through line 10which merges with line 26 leading to the fractionating tower 21.

While there is shown a common fractionating tower 21 for fractionationof cracked products from 'both cracking chambers I8 and 6I, it will beunderstood that the products` from the two cracking zones may besubjected to independent fractionation if so desired. In such case, theproducts from the two cracking operations may be kept separate from eachother.

Returning to the cyclone separator 69, the catalyst separated therein isremoved from the bottom thereof through conduit 1|. In accordance withthe preferred embodiment of the invention, the catalyst so separated ispassed directly through conduit 1I to a catalyst hopper 22 and againused for cracking the fresh feed introduced through line l0 without anyintervening regeneration. If desired, however, a part or all of thecatalyst separated in the cyclone separator 69 may be recycled to thecatalyst hopper 52 feeding catalyst to the cracking chamber 6I, or apart or all of the catalyst removed from the cyclone separator 69 may bepassed to the regenerating circuit through conduit 12.

With respect to the above, it is desired to emphasize that in accordancewith the present invention it is not essential to regenerate thecatalyst after each cracking operation but the catalyst after passingthrough a cracking chamber may be recycled to the same or differentcracking units for a predetermined period before subjecting the same toa regenerating treatment. As a result, the number of regenerations towhich the catalyst is subjected may be reduced with resultant reductionin capacity of the regenerating and purging equipment. Furthermore, inpractical operations it is not possible to obtain 100% recovery ofcatalystfrom the regenerating gas since some extremely f'lne particlesnormally remain in the regenerating gas. By reducing the number ofregenerations to which the catalyst is subjected, loss of catalystduring regeneration can be reduced.

According to the preferred embodiment of the invention, fresh or freshlyregenerated catalyst is first utilized for crackinga relativelyrefractory stock such as a cycle gas oil from the cracking operation andthe catalyst after passing through this process is utilized directlywithout regeneration as catalyst for cracking a less refractory stocksuch as virgin oil introduced into the system through line l0.

While there have been illustrated two separate cracking units operatingmore or less in successive stages, it will be understood that additionalstages may be added to the system as desired. For example, catalystseparated from the cracked products separated in the separator 24 or 69may be passed to .a third cracking circuit without regeneration, or apart may be recycled to the same circuit.

'I'he invention also comprehends the further cracking treatment ofcracked vapors before or after dry separation of powdered materialtherefrom and without any intermediate condensation. For example, a partof the suspension of cracked vapors and catalyst removed from therecycle cracking chamber 6| may be returned through line I3 and iniectedinto the stream of oil psing to the heating coil 58. For illustrativepurposes there has been shown an injector 14 for introducing thesuspension into the oil stream although a fan or other suitable meansmay be substituted therefor. When operating Both methods of operating asjust described have advantages.

By recycling a part of the suspension of cracked vapors and catalyst,the cracking time for a cracking unit of given size can be controlledand additional heat supplied to the recycled suspension tovassist inmaintaining temperature.

, By first separating the bulk of the catalyst in dry state and thenindependently recycling a prtion of catalyst and vapors to the same orseparate circuit, the relative proportions of catalyst and vapors can becontrolled as desired. This is not possible when a. portion of thesuspension of cracked vapors and catalyst is recycled.

Having described the preferred embodiment of the invention, it will beunderstood that it embraces such other variations and-modifications ascome within the spirit and scope thereof.

What is desired to be protected by Letters Patent is:

1. A method of catalytically cracking hydrocarbon oils to form lowerboiling motor fuel products which comprises suspending a cracking inthis way it is desirable to omit use of separator 62.

Likewise a part of the cracked vapors and catalyst suspension from thereaction chamber I8 operating on fresh feed may be returned through line'I5 and injected into the fresh oil feed line AIII passing to theheating coil I2.

As a further alternative a part of the vapors from either the fresh oilor recycle circuit or both may be passed to either one of the twocircuits for further cracking without intermediate condensation. Forexample, a part of the vapors from the vapor line 25 leading from thecyclone separator 24 to the fraotionating tower 21 may be passed throughlines 16 and 11 and transferred either through lines 'I8 and 'I5 to theinlet of heating coil I2 or a part or all may continue through line 19,to the inlet of heating coil 58 for further cracking.

catalyst substantially free of carbonaceous deposit in a stream of oilto be cracked, passing the resulting suspension through a cracking zonemaintained at cracking temperature, keeping said suspension within thezone for a period sumcient to effect the desired cracking thereof,thereafter `.separating the catalyst from cracked products,

suspending catalyst so separated in a stream of oil which is moreamenable to cracking treatment than said rst named stream, passing saidlast named suspension through a cracking zone separate and independentfrom said rst named cracking zone, keeping said suspension within saidlast named cracking zone for a period sutilcient to effect the desiredcracking thereof and fractionating cracked products to separate a motorfuel fraction therefrom.

2. The invention defined in claim 1 wherein cracked products from one ofsaid cracking operations are fractionated to segregate insufficientlycracked constituents above the motor fuel boiling range and the fractionso segregated is em-y ployed as feed stock in said first named crackingstep.

3. The invention defined in claim 1 wherein virgin oil is employed ascharging stock for said second named cracking step and cracked oil isemployed in said first named cracking step.

' 4. The invention defined in claim 1 wherein catalyst separated fromthe second named cracked Vproduct is regenerated to remove carbonaceousdeposit formed thereon and the regenerated catalyst employed in saidfirst named cracking step.

- JOSEPH V. MARANCIK.

HOMER Z. MARTIN.

